Users of portable computers, such as frequent travellers, generally also have a desktop computer back at their office or home and the need often arises to exchange data electronically back and forth between the portable and desktop computers. Traditionally, there are a number of ways this can be achieved. For example, the user could copy data from one computer onto a floppy disc, transfer this disc to the other computer, and then read in the data, always assuming that both computers have compatible floppy disc drives. The foregoing approach is obviously very inconvenient and a much more common approach, illustrated in FIG. 1 of the accompanying drawings, is to interconnect the portable and desktop computers 10, 11 through their serial or parallel ports using a suitable cable 12. Appropriate software running on both computers is then used to effect the desired data transfer. The drawback of this approach is that with current standard serial and parallel port designs, the data transfer rates are low and the mechanics of making the connection are cumbersome (the cables and cable connectors required being relatively substantial and the mating connectors provided on the computers being invariably located in inconvenient positions since for most usages, they are only infrequently accessed).
Another approach to providing inter-connection between a portable and a desktop computer is to use a "docking station" providing a relatively direct connection between the bus systems of the two computers; this generally enhances the data transfer rates achievable but at a significant cost premium in providing the docking station.
A further possibility is to use an infrared link between the two computers as illustrated in FIG. 2; in this case, both the portable computer 10 and the desktop computer 11 are provided with infrared transceivers 14 which when lined up with each other enable an infrared link 15 to be established giving high data transfer rates. This approach has in practice been found to be very sensitive to the correct alignment of the transceivers and cannot currently be considered a robust solution.
Yet another approach is to use a computer network to interconnect the portable and desktop computers. FIG. 3 illustrates one possible arrangement based on a 10BaseT network (see ANSI/IEEE 802.3 standards). In this case, each computer or other DTE (in FIG. 3, portable 10, desktop computers 11) is connected by two UTP (Unshielded Twisted Pair) lines to a corresponding port of a multiport repeater unit 20A, 20B. One UTP line 21 serves to transmit signals from the DTE to the repeater unit and the other UTP line 22 serves to transmit signals from the repeater unit to the DTE. Signals received by the repeater unit at any port are repeated on the outgoing lines of all other ports. A repeater port may also be connected to a corresponding port of another repeater unit to enable expansion of the network. A fiber-optic version of this network arrangement is also known in which each UTP line is replaced by a corresponding fiber-optic cable providing a simplex connection.
Whilst the use of a network to exchange data between a portable and desktop computer provides reasonable data transfer rates (depending on the network technology used), a number of drawbacks still exist in relation to ease of use. In particular, because two UTP lines are used for each connection, care must be taken to ensure that the transmit output of the repeater unit is connected to the receive input of the DTE and that the transmit output of the DTE is connected to the receive input of the repeater unit--in other words, care must be taken to implement a "crossover" function somewhere along the path between the DTE and repeater unit. Unfortunately, a variety of practices exist with crossovers sometimes being built into the MAU (Media Attachment Unit) at each repeater port, sometimes being provided in the cable carrying the two UTP lines, and sometimes being built into the MAU at a DTE. As a result, it is very easy for a non-expert user to effect an improper connection unless the wiring has been previously set up taking into account whether or not the user's portable computer includes an internal crossover.
WO-94/13072 (Farallon Computing) describes one solution to the problem of correctly implementing crossover in a 10BaseT type network. More particularly, an auto-crossover transceiver is described that is capable of sensing which line is a transmit line and which a receive line and correctly interconnecting the lines presented to it. The auto-crossover transceiver is described in the context of a form of 10BaseT type network (see FIG. 4) in which the repeater unit is effectively distributed over the network between a series of auto-crossover transceivers 25 in a way that allows daisy-chaining of the DTEs (in this case, computers 10 and 11A,B,C). Each transceiver is associated with a DTE and receives power from it when the DTE is switched on. When energised, the transceiver operates as a three port repeater, both transferring signals along the daisy-chain of transceivers and exchanging signals with its associated DTE over cable 27 that typically connects to the serial port of the DTE. Each transceiver includes bypass relays which maintain the daisy chain when the corresponding DTE is turned off resulting in de-energisation of the repeater circuitry of the transceiver.
The transceiver 25 can be implemented either as a separate unit (as illustrated in FIG. 4 for computers 11A and 11C), or as a card insertable in a desktop computer (as for computer 11B).
It will be appreciated that with the arrangement described in WO-94/13072, it is a much simpler matter for the user of a portable computer to connect up the portable computer 10 to the network in order to exchange data with a desktop computer 11 (in FIG. 4, the portable computer 10 is shown attached at the end of the daisy chain, depending from the repeater 25 associated with computer 11A). However, whilst the provision of auto-crossover circuitry in the transceivers 25 facilitates use, it represents a cost overhead and even then does not completely obviate the need for crossover cables in certain circumstances.
There thus remains a need for a simple way for a non-expert to interconnect a portable computer with a desktop computer which is capable of supporting high data transfer rates.